This invention relates generally to means for filling an insulated flask with a cryogenic liquid.
In a specific embodiment, this invention relates to means for filling a small, portable, liquid oxygen storage container used for the therapeutic dispensing of oxygen.
There is often need for filling an insulated flask with a cryogenic liquid such as liquid nitrogen or liquid oxygen. One common circumstance in which small insulated flasks are filled with liquid oxygen on a routine basis is in the field of oxygen therapy. There are a number of commercially available liquid oxygen therapy systems, both stationary and portable, to provide oxygen for persons of impaired breathing ability. Such systems typically include a relatively large capacity, stationary home unit and a much smaller portable unit sized to provide from about three to about fourteen hours of continuous oxygen supply. The portable unit is refilled as needed, often one or more times per day, from the larger stationary unit.
The flask used in typical liquid oxygen therapy units is generally cylindrical in shape with a relatively narrow neck and is sized to hold from about one and one half to four pounds of liquid oxygen. It is typically constructed of stainless steel with vacuum insulation as glass is too fragile to withstand the working pressure of some 10 to 30 psi maintained within the flask during use. Also, glass is susceptable to breakage upon moderate impact making it unsuitable for use in a portable unit.
The top of the flask is closed and sealed with a metal flange incorporating conduit means communicating between the interior and the exterior of the flask. One conduit is provided as a liquid fill line. Another is provided to vent gas from the container while a third is connected to a dip tube extending to near the bottom of the flask for withdrawal of liquid oxygen. During refilling of the portable unit from the larger stationary unit, the fill line is connected to a liquid oxygen line from the larger unit through a quick connect coupling to establish open communication between the interiors of the two containers. Liquid oxygen flow is established from the large unit to the portable flask by opening the portable unit vent line.
Because the liquid fill line terminates within the portable flask at a location relatively close to the vent port, there is a tendency for liquid droplets to become entrained in the venting gas and to be carried from the container. Besides being wasteful of liquid oxygen, this condition presents something of a hazard in that liquid oxygen spattering on the skin of a user can produce burns. In addition, liquid oxygen carried out the vent line during filling tends to mask the full flask condition which is ordinarily determined by liquid issuing from the vent line. Consequently, there has been a tendency on the part of some users to only partially fill a portable unit resulting in an important loss of breathing oxygen capacity. It is apparent that an improved filling system for liquid oxygen therapy systems would have significant benefit to the users thereof.